Proton exchange membrane fuel cells show great potential as future source of electrical energy. However, commercialization has been hindered by cost. Membrane electrode assembly (MEA) cost is a significant portion of the cost of the fuel cell stack and is dominated by platinum (Pt) cost, which is used as a catalyst. For the reduction of cost, it is necessary to reduce the required catalyst loading, for which an increase in catalytic activity, particularly for the oxygen reduction reaction at the cathode in a hydrogen/air fuel cell cathode, is necessary.
Significant increases in platinum utilization, and corresponding cost reduction, could be realized if a nanostructured electrode layer is employed, rather than a conventional painted or sprayed electrode. In WO 2012/058425, Pintauro and Zhang describe a nanostructured electrode layer prepared by electrospinning through a metallic needle. Higher performance for a nanofiber MEA with a platinum loading of 0.1 mg/cm2 were reported at 524 mW/cm2 as compared to 519 mW/cm2 for a decal MEA with a platinum loading of 0.4 mg/cm2. Nanofiber electrodes and their production by needle-based electrospinning are also disclosed in W. Zhang et al., ChemSusChem 2011, 4 (12), 1753-1757 and in M. Brodt et al., J. Electrochem. Soc. 2013, 160 (8), F744-F749.
Scaling up production on a needle-based electrospinning system is difficult for multiple reasons and does not lead to high enough fiber productivity for sufficient cost reductions.
It is therefore an object of the present application to provide a process that allows producing such nanofibers by electrospinning on a commercial scale.
It is also an object of the present application that such nanofibers may be produced with consistent and reproducible properties.
Further, it is an object of the present application that such nanofibers are suitable for use as electrode materials in fuel cell applications.
Additional objects become evident from the following description as well as the examples illustrating the present invention.